The present invention relates generally to the improvement of the aerodynamic properties of vehicles, such as trucks, busses, trains, trailers, passenger cars, hovercrafts and motorcycles. More particularly, the invention relates to an airflow control system for ground vehicles, such as bluff-body shaped ground vehicles.
Various solutions are known for improving the aerodynamic properties of a so-called bluff body, i.e. a non-streamlined shape that produces considerable resistance when moving through the air, or a similar medium. Typically, a region of separated airflow occurs over a large portion of the surface of a bluff body. This results in a high drag force and a large wake region. The airflow often exhibits unsteadiness in the form of periodic vortex formation and shedding. Naturally, these effects are undesired. Therefore, to obtain low fuel consumption, bluff-body vehicle shapes should generally be avoided. However, for ground vehicles (trucks, busses and trailers in particular) various regulations place restrictions on the vehicles' maximum outer dimensions. Thus, in order to economize the available vehicle volume, heavy vehicles are normally designed with a shape which to a large extent is a bluff body, i.e. where the front and back surfaces are essentially flat, vertical walls. Instead, to reduce the known drawbacks of such a vehicle shape, airflow control systems may be used to improve the aerodynamics.
The document U.S. Pat. No. 5,908,217 describes a pneumatic aerodynamic control and drag-reduction system for ground vehicles. The system reduces flow separation at the rear portion of a moving vehicle by discharging air at this portion of the vehicle. Blowing outlets are arranged to discharge the air through one or more tangential slots which extend transversely of the upper and/or lower rear portion of the vehicle. Moreover, differential right/left blowing systems may be used to counteract lateral and directional instabilities, for instance when the vehicle is exposed to side winds.
The document U.S. Pat. No. 5,407,245 shows another solution for reducing the drag in the rear region of a vehicle. Blowers emit air through openings in the rear wall of the vehicle to increase the Bernoulli's total pressure behind the vehicle, and thus reduce the air resistance. Here, the blowers are also arranged to suck in air through openings in walls of the vehicle that are located in a so-called eddying zone.
The document U.S. Pat. No. 5,374,013 discloses a method for reducing the drag on a moving body, such as a truck. Here, the vehicle's rear air pressure is increased by forming a pressure shell having a large vortex behind the vehicle. Specifically, a plurality of dynamic flow controllers emit air via a respective high pressure nozzle, which may be rotatable to produce a vortex having a rotation axis parallel to the vehicle's driving direction. The air from the individual flow controllers is then combined into the large vortex.
Thus, various solutions are known for improving the aerodynamic properties of bluff-body shaped vehicles. However, the known strategies either fail to reduce the air drag behind large vehicles sufficiently, and/or these strategies imply an apparatus that is complex, expensive and/or unreliable.